Apparatus for producing high strength calcined gypsum



March 23, 1937. w. s. RANDEL ET AL 2,074,937

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-25 steam to be produced as Patented Mar. 23, 1937 "UNITED STATES APPARATUS FOR PRODUCING HIGH STRENGTH CALCINED GYPSUM Wilbur S. Randel,

Cheshire, Mass., Manvcl C.

Dailey, Maywood, 111., and William M. McNeil, Warren, Ohio, assignors to United States Gyp-.

sum Company, Chicago, 1ll.,

Illinois Original application a corporation of August 5, 1930, Serial No.

473,182. Divided and this application July 5,

1934, Serial No. 1931 This invention relates to the apparatus suitable for carrying out a method of calcining or heating a cementitious product for the purpose of producing a high strength product.

In the Patent No. 1,901,051 of Randel and Bailey, entitled Calcined gypsum, a method and product is described in which gypsum rock is calcined to produce a calcined gypsum having an unusually high strength when cast into shapes.

l0.The present application is a divisional application carved from our copending application Serial No. 473,182, filed August 5, 1930, and covers the apparatus suitable for producing this high an economical manner. The particular features of the calciner per se are disclosed and claimed in patent to McNeil No. 1,897,394.

In the gypsum industry in the ordinary manufacture of kettle-calcined plasters, gypsum rock is ground up to form a powder, this powder is introduced into large kettles, and the kettles are heatedexternally and also by means of internal fire tubes passing through same. The powder is agitatedwhile being heated and the heating causes a result of partial deand the steam evolved hydration of the gypsum,

from the heating of the powder passes up through .the-massof powder, being constantly given off at atmospheric pressure. The results obtained 30 by ordinary kettle calcination are not uniform and the product is apt to vary in strength and composition. The ordinary first settle calcined gypsum is composed of a mixture chiefly of calcium sulphate hemihydrate and soluble anhydrite, with hemihydrate predominating. It is practically impossible to produce pure hemihydrate by the kettle process of calcination. Furthervmore, the strength of the resulting product is comparatively low and does not place it in a field of use comparable to that of Portland cement and certain other cementitious materials. This kettle process is also uneconomical and has a low thermal efiiciency, so that the costof operation is comparatively high.

An object of this invention, therefore, is to provide an apparatus for calcining gypsum under steam pressure so that a uniform product consisting substantially entirely of calcium sulphate o hemihydrate is produced, with a high thermal eificiency.

Another object of the invention is to provide an apparatus for steam calcining "gypsum to produce a calcined gypsum having a high tensile and 55 compressive strength; also to improve apparatus strength calcined gypsum on a large scale and in I is kept hot by live densed 733,800. In Canada March 9.

5 Claims. (o1.v 263-4) for calcining gypsum in other respects hereinafter specified and claimed.

Reference is to be had to the accompanying drawings forming a-partoi this specification, in which Fig. 1 is a flow sheet showing diagrammatically the flow of materials through our improved apparatus,

Fig. 2 is a heat diagram showing the-disposition of the total heat in a method or process suitable for carrying out the present invention,

Fig. 3 is a side elevation of the lower part of our improved apparatus,

Fig. 4 is a side elevation our apparatus,

'Fig. 5 is an end elevation of the lower part of the apparatus, v I

of the upper part of Fig. 6 is acentral sectional elevation through I one of the steam calcination retorts, and

. Figs. 7, 8 and 9 are sectional views through the retort taken on lines 1-1, 8-8 and 9-! respectively of Fig. 6. I

The gypsum rock used in our process is usually obtained by mining or open quarrying and is llazought to the manufacturing plant storage bin rock has the formula CaSO4.2H:O, and after passing through our apparatus, it is calcined and reduced to acementitious powder having formula CaSO4. /2H-.-O. From the rock storage bin l0, the rock goes to a crusher I I and then screen ll, being finally deposited in a secondary rock'storage bin l3, preferably in the form of lumps ranging from to 2" in diameter.

The rock from storage bin I3 is deposited in a series of vertical cylindrical calciners or retorts l4, arranged in parallel for successive operation, so that the net result is a continuous flow of calcined gypsum going through a rotary dryer 15. When the cold rock is first introduced into the retort, hot water from preheated water storage tank IB is runinto the calciner until the. rock is completely submerged and the retort is full of water. This preheated water storage tank J steam introduced into same. The water in this tank is composed both of consteam spent in the chemical reaction and part of the water of crystallization from the gypsum rock which has been converted into free water, and is drained 011 from the calciners into a settling tank l1, and from there into a hot well tank IS. A pump 19 operated by steam engine 20, pumps th hot water from the not well tank it into t e preheated water storage tank It. By submerging the cold rock in hot Fig. 1 ready for procesing. This raw gypsum water run from tank IE to the calciners, the temperature of the rock is immediately raised to a temperature of 100-150 F. This use of the heat in the waste condensate water for preheat- 5 ing the rock, produces marked economies in operation and shortens the calcination cycle. Filling the calciners with hot water at this time also serves to expel any air. contained in the calciner, so that steam subsequently introduced into the calciner after draining-01f the hot water has free action on all parts of the rock in the calciner, thus giving a uniform calcination. A further function of the preliminary water treatment is to wash the dust and fine material from the lumps of gypsum, since this fine material would cake up in the retort and prevent the discharge of the calcined gypsum therefrom. Steam for the calcination, for the water tanks l6 and I6 and for the steam engine 20, is generated by a steam boiler 22 of standard construction. The calcination is accomplished by steam at 15 to 50 pounds per square inch gauge, operating for a period of five to seven hours and at a temperature of 225 to 300 F. A preferred method of operation is through the use of steam at 17 pounds per square inch gauge at a temperature of 253 F. for a period of five to seven hours. The calcined gypsum delivered into the rotary dryer I5 is still in the form of lumps of approximately the same size as the lumps of raw rock first introduced into the calciner. This calcined lump gypsum is then conveyed to a grinding mill 23 of any suitable type for coarse grinding, and then is conveyed to a buhr mill 24 for the purpose of reducing the calcined gypsum to a still finer particle size. Various grinding treatments may be used, followed by screening through the use of a screen 25 to produce products of different grades which are conveyed to a product storage bin 26.

Considering the apparatus now more in detail, conveyor 30, which may be a-s'crew conveyor in a suitable housing, is used for conveying the raw rock from storage bin |3 into a series of inher-connected hoppers 3| located above the row of calciners H, which may be four in number. The top of each calciner I4 is provided with a Y fitting 33 of large diameter, the outstanding arm of which is provided with a valve 34 for regulating the fiow of rock from hopper 3| through the neck 35 of the calciner. The cal ciner I4 is preferable in the form of an elongated, vertical cylinder having suitable outstanding brackets 36 for supporting same on steel framework 31. The Y fitting 33 is provided with a vertical arm 38 having a cover 39 securely bolted thereto, and a stufling box 46 is provided in said cover for making a tight sliding fit with an agitator rod 4| passing upwardly there- 0 through. The agitator rod 4|- is provided on its upper end with a forked bracket 42, and a pin 43 pivotally connects said bracket with a second U shaped bracket 44 formed on the lower end .of a pneumatic vibrator 45 of .standard design. 5 Any other type of reciprocating device may be used for rapidly reciprocating the agitator rod 4| in the stufiing box 40 during the discharge period. The pneumatic hammer 45 is conveniently attached at its upper end to a traveling 7 hoisting crane 46, which travels along a track 41 from one of the hoppers 3| to the adjacent ones, so as to successively actuate different agitator rods 4| in the respective calciners I4. The lower end of calciner I4 is provided with an outlet 75 neck 41, which is connected to a suitable valve 48 for retaining the rock in the calciner l4 and resisting the steam pressure therein.

The lower end of agitator rod 4| is provided with agitator brackets 5| and 52 each of which has preferably a pair of radially extending pivot arms 53. Pins 54 pivotally connect said arms 53 with the inward end'of agitator bars 55, the latter extending radially from the rod 5|. Chains 56 connect the bars 55 intermediate the ends thereof, to a suspension bracket 58 secured to the rod 4| above each of the brackets 5| and 52. By means of this method of suspending the agitator bars 55, the latter may be folded upwardly parallel to the rod 4| when said rod 4| is inserted through the neck 35. The bars 55 then fold downwardly to loosen the rock after the calcination period and cause same to fiow out through the outlet neck 41. The bars connected to brackets 5| and 52 are preferably turned at right angles one to the other to obtain a proper loosening of the rock.

Hot water from the storage tank l6 fiows through pipe 66 and through branch pipes 62 to the upstanding arms 36 of the calciners 4, said calciners being arranged in parallel with individual control valves 6| arranged on branch lines 62. Drain pipes 64 are connected to each of the valve bodies 48 in parallel and deliver into the pressure settling tank I! where the fine gypsum dust or mud settles to the bottom and is cleaned out from time to time. Suitable valves are pmvided on the hot water outlet pipes 64 for contamiling the flow of water. vided with a steam trap 66 leads from the set I tank l1 to the hot well tank l8. Suction pipe 61 extends into the top of tank l8 and is connected to the pump I9. Discharge pipe 68 is also connected to said pump and leads up to the hot water storage tank IS. The tank I6 is provided with an overflow pipe Mia and a drain pipe |6b. Hot water continually accumulates in the system due to condensation of steam as it gives up its heat in performing the chemical reaction of calcining the gypsum, and drain pipe 69 is provided in the tank l8 for passing any excess water to the drain. A pipe 10 provided with a trap 10a, may lead from a drain pipe |1a connected to tank l1 so as to discharge hot water into tank IE if desired.

The steam generated in the steam boiler 22 passes through pipe line 1| and branch line 12 arranged in parallel. A pressure gauge 13 is positioned on each branch line 12, and each ofsaid lines is connected to both the top and bottom of its respective calciner l4, a suitable shut-off valve 14 being provided on each inlet line. The line 1| continues to form a line 15 provided with valve 16,

said line 15 extending downwardly into the hot water storage tank l6 so that the water can be kept hot by the injection of steam to make up heat losses through the insulation on said tank l6. A steam regulator valve 11 is provided on the line 1|, together with a pop valve 18 and a shut-off valve 19. The pop valve 18 is adjusted to blow off at a predetermined maximum pressure, and the pressure reducing valve 11 may be adjusted for delivering steam to the branch lines 12 at,any other lower pressure. An additional pop valve 80 is provided on each of the branch lines '12 in addition to the gauge 13. By this system of valve control on the steam lines leading to the calciners l4, the pressure of steam in said calciners is accurately controlled to produce a product having the highest maximum strength with the greatest manufacturing economy.

A steam line 8| leads from the line 1| to the An outlet pipe 65 t ng engine 20 so as to supply steam "for the operation of said engine. A steam line82leads from the nace 90 for producing engine 20 and delivers steam into the water'contained in the hot well tank I8, so as to maintain a high temperature of said water to make up heat losses through the insulation on said tank I8.

The rotary dryer I5 is of the usual type, consisting of a cylindrical shell inclined slightlyto the horizontal and having circular rings operating on rollers 86. A ring gear 81 is driven by spur gear 88 operated through suitable gearing by a motor 89. A heating furnace 90, preferably of the oil fired type, is connected by duct 9| to the suction of a rotary'fan 92 operated by a motor 93. .A discharge duct 94 connects the fan 92 with the upper end of the'dryer I5, sothat hot products of combustion from the furnace are passed directly through the dryer l5 and then through a duct 95 back to the furnace 90. The furnace 90 is provided with a stack'96 having a control damper, this stack being useful in starting but not during a continuous run. A fresh air inlet pipe 92a is connected to the duct 9| and is provided with a damper 92b for controlling the amount of fresh air continually admitted to the system. A waste gas outlet pipe 95a is connected between the duct 95 and a housing 95b which surrounds the hopper I05 and the retorts I4 to prevent heat losses in the retorts and to prevent or retard recrystallization of the calcined gypsum in the presence of free moisture in the hopper I05. This use of the waste gases as an insulating medium around the calciners results in large heat economies.

The material leaving the lower housing 91 of the dryer I5, passes through a duct 91a having a star feeder 91b, to the mill 23 which is operated by motor 98 to accomplish the preliminary grinding of the material. From the grinder 23, the

ground material passes upwardly through a bucket elevator 99 and then through a screw conveyor I00 to the buhr mill 24 operated by a motor I02. The finely ground material then passes through a conveyor I03 to any other subsequent treating apparatus, such as screen 25.

In order to collect the material flowing from the calciner I4, a hopper I05 is provided below said calciner so as to receive the discharged material from all of the outlet valves 48. In order to insure that all material is cleaned out from the valves 48, a steam line I06 may be attached to each valve for cleaning purposes. A drag chain conveyor I01 passes through the hopper I05 so as to cause movement of the material to the left as seen in Fig. 3, the movement of said conveyor being accomplished by means of a ratchet and pawl mechanism I08 operated by a suitable motor not shown. The conveyor I01 delivers the material into a collecting hopper I09, and said material then passes through a duct I I0 into the upper housing III of the dryer I5. Instead of the furthe hot gases to dry the material, stack gases from the steam boiler 22 may be passed through the rotary dryer I5, as shown in the dotted lines in Fig. 1. The heat diagram shown in Fig. 2, which is provided with explanatory notations, shows that a considerable economy of heat can be accomplished by utilizing the stack gases from the boiler.

In operation, the crushed rock is taken from storage bin I3 through conveyor 30 into feed hoppers 3i. Upon opening valve 34, the crushed rock fiows through pipe 33 and calciner neck 35 into the calciner I4, which is filled substantially full of the crushed rock with the lower valve seven hours, keeping 48 being closed. The calciner I4 is now filled with hot water from tank I6 through pipe 62 to expel the air in the calciner, wash fine material from the lumps of rock and preheat the rock. Steam is now turned on by opening valves 14 on the pipe lines leading into the top and bot--' tom of the calciner |4.- The valve controllin 5 bottom of the calciner is a then run along on the track 41, being supported by the traveling crane hoist 45, until in position over the desired agitating rod 4|. Pin 43 is then slipped into place and the vibration of the pneumatic hammer is started which causes the rapid up and down movement of rod 4| and agitatingbars 55. This agitating movement loosens the calcined rock and causes same to flow outwardly through valve 48 into the receiving hopper I05 above the drag chain conveyor I01. Any number of the calciners I4 may be used to secure a proper cycle so that when the calciners are operated successively, a'substantially continuous stream of calcined rock fiows from the hopper I05.

The calcined rock delivered from the drag chain conveyor I01 fiows into receiving hopper I09 and then through chute IIO into the upper end of the rotary dryer I5. It is important that the transfer of calcined rock from the calciners I4 to the dryer I5 takes place in the shortest possible interval of time so that the temperature of the rock does not drop to a point where recrystallization of the free moisture in the calcined gypsum tal es place. Gaseous products of combustion at a high temperature are continuously passed through the rotary dryer I5 and back through duct 95 to fan 92, some of the waste products of combustion being continuously vented outwardly through pipe 95a. and inside the housing 95b which surrounds the hopper I05 and the retorts I4, new and hot products of combustion being supplied to the system by a furnace 90, preferably fired by oil or other suitable fuel. Fresh'air is continuously admitted to the system through duct 92a. The dryer I5 is continuously rotated and the calcined rock passes downwardly, being delivered from the lowerhousing 91, through duct 91a; and star feeder 9117, into a grinder 23 where preliminary crushing and grinding takes place. The crushed product is then elevated by bucket elevator 99 into a screw conveyor I00 which transfers the material into a grinder 24, preferably of the buhr mill type or other type suitable for fine grinding. From this mill 24, the finely ground material I03 goes to a screen not shown, or other processing equipment, preparatory to storage and final packing for shipment.

We would state in conclusion that while the illustrated examples constitute a practical embodiment of our invention,'we do not wish to limit ourselves preciselyato these details, since manifestly, without departing from the spirit of the-invention as defined in the appended claims.

Having thus described our invention, we claim as new and desire to secure by Letters Patent:-

1. In a gypsum calcining apparatus the combination of a plurality of gypsum steam calciners, a conveyor for receiving calcined gypsum therethe same maybe considerably varied from, a common housing surrounding the calciners and the conveyor, a dryer, a furnace producing hot gasses, means for passing said gases through the dryer, 9. return duct for gases leav- 6 ing the dryer; and a branch duct leading from the latter to the said housing.

2. In a gypsum calcining plant the combination of one or more steam calcining vessels, a hopper for receiving wet calcined gypsum and a 10 conveyor therefor, a common housing around said vessel, hopper and conveyor, a dryer, a furnace yielding hot gases, means for passing said gases through the dryer, a duct for returning the gases to the furnace, and a branch pipe leading from said duct to said housing so as to heat the vessel, hopper and conveyor therein located.

3. In a gypsum calcining plant the combination of one or more steam calcining vessels, a hopper for receiving wet calcined gypsum and a 0 conveyor therefor, a common housing around said vessel, hopper and conveyor. a dryer, a furnace yielding hot gases, means for passing said gases through the dryer, a duct for returning the Bases to the furnace, a branch pipe leading from said ducttosaidhousingloaatoheatthevessel, hopper and conveyor therein located, and means for tempering said gasu by introduction of air 5. In a-gypsum calcining apparatus the com-- bination of oneor more gypsum steam calciners, a conveyor for wet calcined gypsum discharged therefrom. a housing around said conveyor, a dryer, a furnace producing hot gases, and means for passing the hot gases into the dryer-and into the housing. l 

